An inductor (e.g., a choke, coil or reactor) is a passive two-terminal electrical component that stores energy in its magnetic field. Inductors are one of the basic components used in electronics where current and voltage change with time due to the ability of inductors to delay and reshape alternating currents. Inductors are used extensively in analog circuits and signal processing. For example, inductors can be etched directly onto a printed circuit board (PCB) or can be built on integrated circuits (ICs). An inductor is typically made of a wire (or other conductor) wound into a coil, to increase the magnetic field. The coil is wrapped around a core of either air or a ferromagnetic material. When current flowing through an inductor changes, a time-varying magnetic field is created inside the coil and a voltage is induced which opposes the change in current that created it. Inductors have resistance, due to the resistance of the wire and losses in the magnetic core material. Magnetic core material losses contribute to inductor losses at higher frequencies.